A holding brake of the type used on a manipulator normally prevents the two relatively rotatable parts it acts on from rotating. Only when the brake is energized, normally by feeding a fluid under pressure to it, does it allow the two parts to rotate relative to each other. In a manipulator, this brake holds the joints rigid until they are called on to flex or otherwise move.
It is essential that such a brake hold the two parts absolutely rigidly when it is not energized. In addition it should be able to clamp these parts and unclamp them virtually instantaneously. In a multijoint manipulator arm, extreme precision of operation is essential because displacement errors in one joint are amplified by those in another, so that a seemingly tolerable error at one location can lead synergistically to an intolerable one at another.
The standard such brake has a disk mounted on one of the parts and brake elements that can clamp this disk. Typically the disk is somewhat flexible, that is it can be elastically deformed to a limited degree. The disk is clamped by a movable brake element against a fixed element to arrest the rotating and non-rotating parts relative to each other. Teeth between the brake elements and the parts carrying them prevent them from moving relative to this part.
The considerable axial play that must be provided to both sides of such an axially deformable disk, as well as the play between the teeth and the parts they interconnect, frequently make it impossible for the brake to close as rapidly and to hold as solidly as is necessary. What is more, such brakes frequently are very noisy, emitting a clank each time they are actuated, so that operation of a manipulator equipped with them is fairly noisy.